1. Field of the Invention
The present invention relates to a cell, a connected-cell body, and a battery module using the same, and more particularly to a cell for reducing the internal resistance, a connected-cell body, and a battery module using the same.
2. Description of Related Art
A conventional battery module for providing a required electric power capacity by connecting a plurality of cells is constituted such that a plurality of individual prismatic cells are placed while longer side surfaces of their battery case are opposingly brought into contact with each other, end plates are provided outside of the battery cases of the cells on both the ends, and the cells are integrally connected by binding with a tie band. Also, leads are pulled out upward from the top ends of electrode plates in the individual cells, the leads are connected with terminals provided on a cover of the battery case, and then the terminals are connected with each other between the cells with connection plates.
As a result, since connection paths between the cells are long, and the number of connection points is large, resistance caused by constitution parts including connection parts becomes high. A ratio of this part resistance to a reaction resistance caused by a battery reaction among a positive electrode plate, a negative electrode plate, and electrolyte reaches 40:60 to 50:50. Since this large internal resistance increases heat generation, increasing the output and enhancing life characteristics are seriously obstructed. Also, since the connection constitution between the cells is complicated, and the number of the parts is large, the cost also increases.
In light of the foregoing, the present applicant previously proposed a battery module 101 including a plurality of cells 102 as shown in FIG. 16 and FIG. 17. The reference numeral 103 denotes a prismatic battery case which is formed as a flat rectangular solid. This battery case is constituted by integrally connecting a plurality of battery cases 104 in prismatic shape including a short side surface and a long side surface while the short side surface is mutually shared as a partition wall 105. Openings on the top surface of the individual battery cases 104 are closed by a single cover 106. Connection holes 107 are formed on an upper part of the outside short side surfaces of the battery cases 104 on both the ends, and on an upper part of the partition walls 105 between the individual battery cases 104.
The individual battery cases 104 store an electrode plate group 108 constituted by laminating a rectangular positive electrode plate and a rectangular negative electrode plate with a separator interposed between them in addition to electrolyte, thereby forming a cell 102. The positive electrode plate and the negative electrode plate of the electrode plate group 108 protrude from the sides opposite to each other to form leads 109a and 109b for the positive electrode plate and the negative electrode plate. Collector plates 110a and 110b are respectively connected with the side edges of the individual leads 109a and 109b by welding.
A connection protrusion 111 to be engaged into the connection hole 107 is formed at an upper part of the collector plates 110a and 110b. The connection protrusions 111 of the positive and negative collector plates 110a and 110b are connected by welding between the neighboring battery cases 104. Also, positive and negative connection terminals (terminal poles) 112 are installed into the connection holes 107 on the outer short side surface of the battery cases 104 on both the ends. Then, a connection protrusion 113 of the connection terminal 112 is connected with the connection protrusion 111 of the collector plate 110a or 110b by welding. Consequently, the plurality of cells 102 stored in the prismatic battery case 103 are connected serially, and a power is provided between the connection terminals 112 on both the ends.
In addition, communication passages 114 for equalizing the internal pressure of the individual battery cases 104, safety vents (not shown) for releasing the internal pressure in the individual battery cases 104 when the pressure increases more than a certain value, and a sensor installation hole 115 for installing a temperature sensor for detecting the temperature of a cell 102 are provided on the cover 106.
With the constitution shown in FIG. 16 and FIG. 17, the current-carrying paths from the positive electrode plate and the negative electrode plate to the leads 109a and 109b, and the collector plates 110a and 110b are short. On the contrary, since tips of the connection protrusions 111 on the top end of the collector plates 110a and 110b are connected with each other at the one point by welding as arrows in FIG. 18 show, the connection path is detoured, thereby increasing the length of the connection path. Further, since the connection point is one, the internal resistance increases. Also, as described above, since the connection path is detoured, large amount of current flows through the electrode plate group 108 close to the connection part of the collector plates 110a and 110b while small amount of current flows through the electrode plate group 108 far from the connection part as white arrows with black boarder show. Consequently, the distribution of the current flowing through the electrode plate group 108 becomes uneven, thus the entire electrode plate group 108 does not present uniform power generation capability, and consequently the loss increases.